Re: Intercept Algorithms and V1.
- From: "Geoffrey Sinclair" <gsinclairnb@xxxxxxxxxxxxx>
- Date: Thu, 2 Apr 2009 00:46:48 +1100
<eunometic@xxxxxxxxxxxx> wrote in message
news:a6344109-dd94-422e-842b-679dab8204e0@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
The German Navy used a burst message system that could send 7
baudot characters (it was enough with code tables) in 0.46 seconds.
This sounds like the late war Kurier system.
By the way this version of the burst idea started testing
in August 1944, but was never deployed beyond test beds.
http://users.telenet.be/d.rijmenants/en/kurzsignale.htm
It was compromised due to an earlier u-boat capture in which code
documents revealed its existence so allies were occasionally able to
listen to it (via photgrpahs of oscilicopes) especially when the standard
enigma 'shark' code base station was used to transmit the frequencies
to use for the day to the subs also since its 7 character message was
short and encrypted by shark it actually helped crack into shark since
it often transmitted weather data and this was often an excellent crib.
Shark was the allied name for the enigma system the Atlantic U-boats
began using from 5 October 1941. It was promptly cracked. Called
Triton by the Germans. On 1 February 1942 it was the system in use
when the fourth code wheel was introduced.
The allies cracked this in December 1942, though it took months
before it was read consistently. The cracking was helped by code
books taken from U-559 when it was sunk in the Mediterranean.
Cribs were very useful while the allies had only 3 rotor bombes
to run, the 4 rotor bombes arrived in mid 1943 and from around
September 1943 on they meant the allies had usually broken the
keys within 24 hours.
One of the first items discovered was the Germans were reading the
allied "Convoy Code". It took until June 1943 for the allies to be
able to change the code.
The physical transmitter is not the code. The allies understood
the short message idea and countered it.
Its purpose was to significantly reduce the effectiveness of Huff Duff
which it could do quite well.
Except the allied HF/DF system was upgraded during the war with
automatic scanning, which helped catch smaller signals, scanning at
20 times per second if I remember correctly.
What did help the U-boats was strict radio silence when in a patrol line,
enforced from April 1943 and the stopping of wolf pack tactics and the
associated signalling.
Huff Duff wasn't the problem ultra was
so kurier adressed the wrong problem.
This is rather wrong actually, the wolf packs were needed if the
Germans were to break the supply lines to England. HF/DF
was useful in a strategic sense, giving an idea of numbers and
locations, and highly useful in a tactical situation for the escorts,
as experienced operators could gain an idea of how close the
U-boat was, things like whether they were in the "ground
wave", as well as signal strength. If there was air escort the
aircraft could run down the bearing.
The less signalling the more Ultra played a part.
My assesment is that though
ingenious it was belated,
What a surprise about the ingenious part.
could have been combined with a bit of
frequency agillity to improve its LPI (low probability of intercept)
Ah yes, the 1950's and 1960's technology given to the Germans.
and most of all needed to be used with its own seperate code system.
The whole point of the burst system is to use it all the time, one
signal in burst and one in normal speed does not make the U-boat
much safer from direction finding. So the code in use would have
been the standard U-boat one.
Rommel used a secure radio voicelink from Tunisia to Berlin based
on a spread spectrum techniques: the pseudo random signal was
encrypted on a rotating glass disk through which a photocell shone.
The voice signal was multiplied with the pseudo random sequence
which being a 'squarish wave' actually consists of a series of sine
wave of differing frequencies, amplitudes and phases that could only
be demodulated to its original form at the other end by a glass disk
of the same type.
I like the assumption it could not be demodulated.
It was obviously a fairly compact device.
I really like the assumption it was "fairly compact". Several transmitters
coupled together plus the electronics to encode and determine which
transmitter to use are hardly compact using WWII technology. Plus
of course there are the power requirements.
An experimental German radar called "Kugelschale" used pulse chirping
to spread and expand a radar pulse into a unique pulse which had a
range of time varying frequencies across a range of frequencies to
provide both coherent Doppler for resolution of chaff and to
distribute radar pulse energy over a broad enough range of frequencies
to avoid both noise or spot jamming.
The idea was being trialled in a laboratory.
Kuglelschale means 'layered
sphere' (like an onion) and the radar had 75m thick 'skins' that could
be scaned to resolve moving targets against stationary ones while
igoring stationary one.
75 metres sounds rather a lot.
Also note the window clouds were usually not stationary given the
general realities of winds at altitude.
Reisslaus was an experimental airborn radar
that again used doppler to avoid chaff and pulse to pulse frequency
hopping to avoid jamming. Both these units were ground based late
war circuit tests rather than actual devices.
Note in the Eunometic world a German planning to build a device
counts as a working device.
There are indeed a few 1940s patents by Proffessor E Huttman of
Germany re spread spectrum and pulse chirping.
Like other countries, the trouble is making it work.
Late versions of the Wurzburg Riesse radar had automatic frequency
changing though this was not pulse to pulse tanking just over 10
seconds.. In the 'giant' form Wurzburg (with the 7m aerial) this
circuit and the giant aerial seems to have been enough to get through
allied jamming and window.
The short answer here is no. The allies could change jamming
frequencies as well.
As policy radars in 3 FLAK towers were
maintained at the highest and latest technical level.
And were continually jammed, especially the fire control radars, the
statistics on damaged RAF bombers shows that quite well. The
problems in making fighter interceptions showed the longer range
radars also had problems.
The Kehl-Strasberg radio control system used on Fritz-X and Hs 293
MCLOS guidence continually had its frequencies expanded. The final
combat versions were capable of one in flight frequency change to
avoid jamming. This is probably why they were still able to hit
allied ships during the Normandy landings.
The last time this claim was made the ships listed were either not at
Normandy or sunk by other means. So what is the sunk ships list
this time?
And for that matter when were the daylight raids in good enough
weather to guide the missiles?
The Germans had successfully developed ferrite magnetic tape recorders
(developed by them during the war) and were also therefore able to use
endless loop tapes with accurately spaced multiple read/write heads to
correlate seemingly dispersed and random signals to reconstruct a
coherent message or command. This was how they were planning to pass
corrections to advanced guided versions of the V1.
Yet another idea that was not used.
Certainly there was some awareness of the techniques on the German
side though much of this known how was lost due to the dispersion of
the German technical community, destruction of documents and
institutions.
Translation Eunometic wants to believe the Germans did more but without
proof the idea is to pretend the proof was lost.
Geoffrey Sinclair
Remove the nb for email.
.
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